A new degree of complexity in establishing and maintaining communications links has been brought about by the introduction of new mutually exclusive communications modes.
Waveforms which cannot be simultaneously received through a single receiver whose front-end has a single RF translation signal path, are defined as "mutually exclusive" of each other. For purposes of this document, mutual exclusivity is characterized by virtue of the different frequency agility requirements placed upon the receiver's RF tuner. For purposes of illustration, but not as a limitation, conventional fixed frequency HF single sideband (SSB), channel scanning automatic link establishment (ALE) (described in detail in U.S. Pat. No. 4,328,581, herein incorporated by reference), and frequency hopping signals are three examples of different waveforms (communications modes) that are considered mutually exclusive.
A receiver and transmitter configured as a conventional transceiver can either receive or transmit as determined by the state of the Push-to-Talk (PTT) key but can not do both simultaneously. All operations described herein assume stations configured as transceivers unless otherwise stated.
A first given station may periodically need instantaneous PTT communications with a particular second station while both stations are operating in a network comprised of a plurality of additional stations, all of which are operating in a scanning ALE communications mode. Prior art allows an ALE link to be established automatically within tens of seconds between any two stations in the network. However, if instant PTT communications is required between two particular stations, those stations must leave the ALE scanning mode and remain on a propagating fixed frequency to avoid the linking delays. The two stations, now operating in a mutually exclusive mode from the other network stations, will not be able to monitor the other scanned ALE channels for calls or sounds which greatly reduces their availability for communications with other network stations. Furthermore, as time passes and propagation conditions change, the selected fixed frequency may no longer support skywave communications between the two stations. Thus, what was an instant PTT link the last time it was used, may now be a total outage. It will become evident to one of the two stations that there has been an outage when communications is attempted and fails. The other station may not be aware of the failure for some time until it also attempts to communicate with the other station and fails. The first station is helpless to reestablish the link until the second station also recognizes the outage and returns its system to the ALE scanning mode. Lack of current link quality analysis (LQA) data decreases the probability of first time success on the ALE call back which further aggravates the link reestablishment delay problem following an outage.
Because of the "scanning" nature of HF ALE waveforms and linking protocols, operation in the ALE mode precludes the use of the HF radio transceiver for monitoring conventional fixed frequency (non scanning) HF single sideband (SSB) channels or operation in a frequency hopping mode. Likewise, because of the rapid retuning requirements placed on a transceiver reflecting the nature of a frequency hopping waveform, operation in a frequency hopping mode precludes the use of the HF radio transceiver for monitoring conventional fixed frequency HF SSB or ALE scanning modes.
A prior art solution to the above problems requires the use of multiple HF transceivers (one for each different waveform or communications mode to be monitored), multiple antennas (or appropriate antenna switching and transmit antenna interlock circuits to allow the shared use of one antenna) and an appropriate system-level means of selecting which HF transmitter is to be keyed when a transmission is to be made.
Accordingly, there is a present need for an HF radio transceiver which can monitor multiple waveforms simultaneously and dynamically allocate its transmitter to the appropriate waveform according to the circumstance.